A series of new lanthanide fumarates displaying three types of 3-D frameworks

Abstract

A series of lanthanide fumarates [Sm₂(fum)₃(H₂fum)(H₂O)₂] (1, H₂fum = fumaric acid), [Ln₂(fum)₃(H₂O)₄]·3H₂O {Ln = Tb (2a), Dy (2b)} and [Ln₂(fum)₃(H₂O)₄] {Ln = Y (3a), Ho (3b), Er (3c), Tm (3d)} were prepared by the hydrothermal method and their structures were classified into three types. The 3-D framework of compound 1 contains a 1-D infinite [Sm–O–Sm]_n chain built up from the connection of SmO₈(H₂O) polyhedra sharing edges via three –COO group bridges of fumarate ligands, which is further constructed into a 3-D network structure with three kinds of fumarate ligands. Compounds 2a–b are isostructural and consist of a 3-D porous framework with 0-D cavities for the accommodation of chair-like hexameric (H₂O)₆ clusters. Compounds 3a–d are isostructural and have a 3-D network structure remarkably different from those of 1 and 2a–b, due to the different coordination numbers for the Ln³⁺ ions and distinct fumarate ligand bridging patterns. A systematic investigation of seven lanthanide fumarates and five reported compounds revealed that the well-known lanthanide contraction has a significant influence on the formation of lanthanide fumarates. The magnetic properties of compounds 1, 2b and 3b–3d were also investigated.